1. Field of the Invention
The present invention relates to a dynamic light scattering measurement apparatus capable of performing dynamic light scattering measurement of particles in a sample medium.
2. Description of the Related Art
The dynamic light scattering measurement method is a method for examining dynamic properties of scatterers by irradiating light to a medium such as a suspension and detecting the time fluctuation of the intensity of the scattered light scattered from the scatterers in the medium using a time correlation function and a power spectrum, and this method is widely used for particle diameter measurement, aggregation measurement and the like.
However, this method is used with respect to a diluted medium to which the single scattering theory (a theory that light scattered once can be detected without being scattered again by other particles) is applicable. And therefore, this method has such a disadvantage that, when the concentration of a medium is too high to ignore influences of multiple scattering (a phenomenon that once scattered light strikes other particles and is scattered again), dynamic properties of the particles detected based on the single scattering theory are different from the real dynamic properties.
From this reason, recently, such reports have been made that the time correlation function and the power spectrum of scattered light are measured with using an interferometer having a low coherence light source.
Using such an interferometer having a low coherence light source, only the scattered light component from a specified portion substantially equal to the light path length of a reference light can be extracted, so that only the single-scattered component of scattered light can be selectively detected from a high concentration medium.
Based on this, time-fluctuating spectrum of scattered light and correlation function can be detected, and thereby dynamic properties of particles of a high concentration medium can be measured.
Using the abovementioned interferometer having a low coherent light source, scattered light from particles in the deeper portion of a sample medium can be measured by setting the light path length of the reference light the longer. However, since light decays largely in a high concentration medium, it is not preferable to select so deep a portion in the sample medium.
Consequently, it is requested to establish a standard for setting a suitable range of the light path length of the reference light in order to effectively extract scattered light from a sample medium.
An object of the present invention is to prove that, in the spectrum measurement of a multiple scattering medium, the spectrum of the multiple scattering medium is dependent on the light path length, and thereby to provide a dynamic light scattering measurement apparatus using phase modulation type interference method capable of measuring with high precision the dynamic properties of a high concentration medium based on the scattered light from the high concentration medium.